Paul on Friday told an annual gathering of conservative leaders and activists that Obama had violated the Constitution by backing drone strikes on American citizens and the collection of millions of Americans' telephone records in a secret surveillance program.

Paul quoted the Founding fathers as well as Pink Floyd. He urged conservatives to join his efforts to stop what he deemed unconstitutional measures.

In his words: "Government unrestrained by law becomes nothing short of tyranny."

The Kentucky senator was an afternoon speaker Friday at the annual Conservative Political Action Conference in suburban Maryland. He is among several prospective presidential candidates at the three-day conference and attracted the largest crowd so far.